<%@ page import="java.util.ArrayList" %>
<%@ page import="java.util.List" %>
<%@ page import="com.atguigu.bean.User" %><%--
  Created by IntelliJ IDEA.
  User: zsh
  Date: 2020/9/10
  Time: 8:12
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<%
    User user = null;
    String username = "";
    List<String> list = new ArrayList<String>();
    pageContext.setAttribute("user", user);
    pageContext.setAttribute("username",username);

    pageContext.setAttribute("list",list);
%>
判断域对象中是否有属性名为 user 的数据：
${not empty pageScope.user}<br>
判断域对象中的username所对应的数据是否为空 ${not empty pageScope.username}<br>
判断域对象中的list所对应的集合是否为空${empty pageScope.list}<br>
<br><br><br><br><br>


判断域对象中是否有属性名为 user 的数据：${pageScope.user==null}<br>
判断域对象中的username所对应的数据是否为空 ${pageScope.username.length()==0}<br>
判断域对象中的list所对应的集合是否为空${empty pageScope.list.size()==null}<br>


</body>
</html>
